Thursday, August 31, 2006

Hurricane John and Arizona weather

Today in southern Arizona is much like yesterday wrt CAPE. However, the steering winds today are light westerly and there is little directional shear above 500 mb. Thus, another day favoring heavy storms over the mountains and lots of anvil cloud over many low elevation areas.

Hurricane John is moving toward southern tip of Baja as a strong Cat 3, or even a Cat 4, hurricane. Yesterday's discussion remains essentially valid. Initially, the pressure gradient at low-levels becomes cross or down the Gulf of California. The NAM actually predicts light northerly winds at 850 mb over southern Arizona tomorrow afternoon, but as John moves westward away from the tip of Baja, a rapid push of moisture up the GoC should occur, probably coming into the U.S. late Friday night. A turn toward the west sooner than NHC predicts would bring moisture northward more quickly.

On Saturday the moisture influx from John should interact with a strong back-door cold front coming westward across the Continental Divide, producing perhaps the most intense storms of the weekend.

There are too many complexities in the situation to have much forecast confidence beyond Saturday and even the details of Saturday are difficult to anticipate, since the flow may become strongly downslope in the local Tucson area.

A final possible complication to at least consider is that the GFDL model continues to predict that Hurricane John will move directly into the GoC and make landfall on the western coast of Mexico.

1 comment:

  1. Anonymous2:12 PM

    Looking at satellite trends and station data, the lowest pressures are on the east side of the gulf of california...still think this one will be heading along the same direction as it is now and enter into the southern gulf and possibly up to Los Mochis area before landfall.

    Pat Holbrook

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